1. Field of the Invention
The present invention relates to a liquid crystal display module, more particularly, a liquid crystal display module for improving display quality.
2. Description of the Related Art
In general, a liquid crystal display (LCD) device includes a liquid crystal display module and a driving circuitry for driving the liquid crystal display module. The liquid crystal display module includes a liquid crystal display panel having liquid crystal cells arranged in a matrix between two glass substrates, and a back light unit for irradiating light through the liquid crystal display panel. In addition, optical sheets for directing the light from the back light unit toward the liquid crystal display panel in a vertical direction are arranged on the liquid crystal display module. The liquid crystal display panel, the back light unit and the optical sheets should be engaged with each other so as to be integral to prevent light loss and protected from damage due to external impact. Thus, a case is provided for the LCD device to enclose the back light unit and the optical sheets as well as the edges of the liquid crystal display panel.
FIG. 1 is an expanded perspective view illustrating the related art liquid crystal display module. FIG. 2 is a sectional view illustrating the liquid crystal display module taken along line I–I′ in FIG. 1. Referring to FIGS. 1 and 2, the liquid crystal display module 1 includes a main support 14, a back light unit and a liquid crystal display panel 6 stacked inside of the main support 14, and a top case 2 for enclosing the edge of the liquid crystal display panel 6 and the side surface of the main support 14.
The liquid crystal display panel 6 includes an upper substrate 5 and a lower substrate 3. Liquid crystal materials are injected between the upper substrate 5 and the lower substrate 3. The liquid crystal display panel 6 is provided with a spacer (not shown) for maintaining a cell gap between the upper substrate 5 and the lower substrate 3. The upper substrate 5 of the liquid crystal display panel 6 is provided with a color filter, a common electrode and a black matrix(not shown). Signal lines, such as a data line and a gate line (not shown) are formed on the lower substrate 3 of the liquid crystal display panel 6. A thin film transistor (TFT) is formed adjacent to a crossing of the data line and the gate line. The TFT switches a data signal from the data line to the liquid crystal cell in response to a scanning pulse (i.e., a gate pulse) from the gate line. A pixel electrode is formed in a pixel region defined between the data line and the gate line.
A pad area is formed at one side of the lower substrate 3 and has pads connected to each of the data line and the gate line. A tape carrier package (not shown) having a driver integrated circuit mounted thereon for applying driving signals to the TFT is attached onto the pad area. The tape carrier package applies data signals from the driver integrated circuit to the data lines. Further, the tape carrier package supplies the scanning signal to the gate line. An upper polarizing sheet is attached onto the upper substrate 5 of the liquid crystal display panel 6 and a lower polarizing sheet is attached onto of the rear side of the lower substrate 3 of the liquid crystal display panel 6.
The main support 14 is made from a mold material, and its inner lateral wall is molded into a stepped coverage face. The stepped coverage face has a securing part in which the back light unit and the liquid display panel 6 are disposed. The liquid crystal display panel 6 and the back light unit are stacked in the securing part of the main support 14.
The recent trend in the back light unit is towards small size, thin thickness and lightweight. Pursuant to this trend, an LED array has been used as a light source, which is advantageous in a power consumption, thickness, weight and brightness in comparison with a fluorescent lamp that is used as a light source for the back light unit.
The back light unit includes: first and second light guide plates 10 and 20, which are stacked in two layers to face the liquid crystal display panel 6; a first light-emitting diode(LED) array 30a arranged to face one side surface of the first light guide plate 10; a second LED array 30b arranged to face the other side surface of the second light guide plate 20; a reflection sheet 12 arranged on a rear surface of the first light guide plate 10; and a plurality of optical sheets 8 stacked between the second light guide plate 20 and the liquid crystal display panel 6. FIG. 3 is a perspective view illustrating the related art light-emitting diode array. The first LED array 30a includes a plurality of LED driving circuits 34a and a printed circuit board (PCB) 32a on which the LED driving circuits 34a are arranged in parallel, as shown in FIG. 3. Each of the LED driving circuits 34a includes an LED, which functions as a point light source, for emitting an incoherent light color, such as a red light, a green light or a blue light, and a control circuit for controlling the emission of the LED. The first LED array 30a is arranged to face the incident surface provided at one side surface of the first light guide plate 10.
The second LED array 30b has configuration elements and a structure identical to that of the first LED array 30a shown in FIG. 3. For instance, the PCB 32 and the plurality of LED driving circuits 34a of the first LED array 30a correspond to PCB 32b and a plurality of LED driving circuits 34b of the second LED array 30. Accordingly, an explanation of the second LED array 30b will be substituted with the explanation of the first LED array 30a. The second LED array 30b is arranged to face the incident surface provided at the other side surface of the second light guide 20.
Lights generated from each of the first and the second LED arrays 30a and 30b are irradiated to the first and the second light guide plates 10 and 20 via the incident surfaces of the first and the second light guide plates 10 and 20, respectively. Each of the first and the second light guide plates 10 and 20 converts a path of the light incident from each of the first and the second LED arrays 30a and 30b to be perpendicular to the liquid crystal display panel 6.
A scattering pattern 15 is provided on a rear surface of the other side of the first light guide plate 10 and is separated from the first LED array 30a. The scattering pattern 15 reflects the light irradiated from the first LED array 30a via the incident surface of the first light guide plate 10 and scatters the lights to diffuse toward the second light guide plate 20. The scattering pattern 15 is separated by the designated distance d1 from the incident surface of the first light guide plate 10 to mix the red, green and blue color lights irradiated from the first LED array 30a so as to convert them into a white color.
A scattering pattern 25 is provided on a rear surface of the other side of the second light guide plate 20 and is separated from the second LED array 30b. The scattering pattern 25 reflects the light irradiated from the second LED array 30b via the incident surface of the second light guide plate 20 and scatters the light to make it diffuse toward the optical sheets 8. The scattering pattern 25 is separated by the designated distance d2 from the incident surface of the second light guide plate 20 to mix the red, the green and the blue color lights irradiated from the second LED array 30b into a white color.
The reflection sheet 12 is located at the rear surface of the first light guide plate 10, and serves to re-reflect the light incident thereto through the rear surface of the first light guide plate 10 into the first light guide plate 10, thereby reducing a light loss. In other words, the light irradiated on each of the first and the second light guide plates 10 and 20 that progresses toward a lower surface of the first and the second light guide plate 10 and 20 is reflected by the reflection sheet 12 to be redirected toward the liquid crystal display panel 6.
Each of the optical sheets 8 diffuses the lights provided from the first light guide plate 10 and the second light guide plate 20 and converts the paths of the lights to be perpendicular to the liquid crystal display panel 6, to thereby improve light efficiency. To this end, a lower diffusing sheet is stacked on the second light guide plate 20 for diffusing the light provided from the first and second light guide plates 10 and 20 into the entire area, first and second prism sheets for converting a progress angle of the light diffused by the lower diffusing sheets to be perpendicular to the liquid crystal display panel 6, and an upper diffusing sheet for diffusing the lights going through the first and second prism sheets to irradiate light onto the liquid crystal display panel 6. Thus, the lights from the first and second light guide plates 10 and 20 are irradiated via the optical sheets 8 to the liquid crystal display panel 6.
The top case 2 is manufactured in a shape of a square band having a plane part and a side part. The top case 2 encloses the edge of the liquid crystal display panel 6 and the main support 14.
As described above, since the LED driving circuits 34a and 34b emit incoherent colored lights, such as red light, green light and blue light, the LED driving circuits 34a and 34b are separated by at least a designated distances d1 and d2 from each of the first and the second light guide plates 10 and 20 to mix the red, green and blue lights into white light. For this reason, the scattering patterns 15 and 25 provided at the first and second light guide plates 10 and 20 are formed to separated by the designated distances of d1 and d2 from the incident surfaces of the first and the second light guide plate 10 and 20, respectively.
If the LED driving circuits 34a and 34b emitting the red, green and blue lights are used as light sources, then brightness of the lights from the first and second light guide plates 10 and 20 becomes uneven because partial areas of the first and second light guide plates 10 and 20 are used as regions in which the red, green and blue lights are mixed into a white light whereas the lights are scattered only at the remaining areas. In other words, light 36a emitted from the LED driving circuit 34a of the first LED array 30a arranged at the side surface of the first light guide plate 10 is scattered by the scattering pattern 15 provided at the first light guide plate 10 and the scattered light 38b then progresses toward the liquid crystal display panel 6. Also, light 36b emitted from the LED driving circuit 34b of the second LED array 30b arranged at the side surface of the second light guide plate 20 is scattered by the scattering pattern 25 provided at the second light guide plate 20 and the scattered light 38b then progresses toward the liquid crystal display panel 6.
The above-mentioned back light unit of the related art liquid crystal display module 1 has a drawback of increased thickness and weight since a set of two light guide plates 10 and 20 are used to obtain a uniform brightness. Furthermore, since the light 36a from the first light guide plate 10 goes through the second light guide plate 20, the brightness of the related art liquid crystal display module 1 becomes lower. The lowered brightness deteriorates a display quality of the liquid crystal display module 1.
FIG. 4 shows an arrangement of a back light unit employing a color mixing light guide plate. To solve the problems that the thickness of the back light unit becomes thick and brightness becomes uneven, there has been proposed a back light unit employing a light guide plate 40 for a color mixing as shown in FIG. 4. The color mixing light guide plate 40 doesn't require an area in which the red, green and green lights are mixed into white light as in the related art light guide plates 10 and 20 shown in FIG. 2. Thus, the back light unit can be made with one color mixing light guide plate 40 and therefore, it is possible to decrease the thickness of the back light unit. Further, by arranging the first and the second LED arrays 30a and 30b shown in FIG. 1 at both side surfaces of the color mixing light guide plate 40, the brightness of the light irradiated to the liquid crystal display panel 6 can be uniform. However, in the arrangement that a light source is arranged at the side surface of the color mixing light guide plate 40, light efficiency is low, so that brightness is lower accordingly. Thus, such an arrangement is still disadvantagous in that display quality of the liquid crystal display module deteriorates.